4-5 XLEE-U 解:(1)Icz-2KE BE 根据戴维南定理将原电路化简 U。R L Rc+Ru RI R R RC=R‖R CE20 cC-Ic20Rc+0.7 (2)K nd⊥RB++B·2R CMR =-|= EE C 2(Rg+/) BRd=2(RB+re), roc=Ro4-5 i d B b e O C C B b e B b e E u C u d CMR CE Q CC C Q C C C L C L CC L CC E E E B E C Q R R r R R R r R r R A A K U U I R R R R R R U R U R U U I = + = + + + • = = = − + = + = − =  (3) 2( ), 2( ) 2 (2) | | 0.7 || 2 1 1 ' 2 ' 2 ' ' 2  根据戴维南定理将原电路化简 解：（）